Operational amplifier

ABSTRACT

An operational amplifier 1 comprises transistors Q1 and Q2 forming an input stage, and input resistors R1 and R2 which form a filter together with parasitic capacitors C1 and C2 accompanying the transistors Q1 and Q2. Resistance values R of the resistors R1 and R2 may be set to R=1/(2π·fc·C), where C is the capacitance value of each of the parasitic capacitors C1 and C2, and fc is the target cutoff frequency of the filter. The operational amplifier 1 may also include a power supply resistor R0 which forms a filter together with a parasitic capacitor C0 accompanying a power supply line.

TECHNICAL FIELD

The invention disclosed herein relates to an operational amplifier.

BACKGROUND ART

Operational amplifiers have conventionally been used in various fields.

An example of the conventional technology related to this is disclosedin Patent Document 1 identified below.

LIST OF CITATIONS Patent Literature

Patent Document 1: Japanese Patent Application Published as No.2011-9800

SUMMARY OF THE INVENTION Technical Problem

However, the conventionally used operational amplifiers still have a lotto improve in terms of their noise characteristics. In particular, inthe fields of industrial appliances and in-vehicle appliances, with theincrease of the number of electronic components and the increase of thedensity of components, there has been growing demand for improvement ofnoise characteristics of operational amplifiers.

An object of the invention disclosed herein is, in view of the abovedescribed problems found by the inventors of the present invention, toprovide an operational amplifier having excellent noise characteristics.

Means for Solving the Problem

An operational amplifier disclosed herein includes a transistor formingan input stage, and an input resistor forming a filter together with aparasitic capacitor of the transistor (a first configuration).

Preferably, in the operational amplifier having the first configuration,a resistance value R of the input resistor is set based on a capacitancevalue C of the parasitic capacitor and a target cutoff frequency fc ofthe filter such that R=1/(2π·fc·C) (a second configuration).

Preferably, the operational amplifier having the first or secondconfiguration further includes a power supply resistor which forms afilter together with a parasitic capacitor of a power supply line (athird configuration).

Preferably, a semiconductor device disclosed herein includes theoperational amplifier having any one of the first to thirdconfigurations, a reference current setting portion configured to set areference current of the operational amplifier, a power supply line laidbetween a power supply terminal and each of the operational amplifierand the reference current setting portion, a ground line laid between aground terminal and each of the operational amplifier and the referencecurrent setting portion, and a reference current setting line laidbetween the operational amplifier and the reference current settingportion (a fourth configuration).

Preferably, the semiconductor device having the fourth configurationfurther includes a capacitor connected between the power supply line andthe reference current setting line (a fifth configuration).

Preferably, in the semiconductor device having the fifth configuration,the capacitor is a parasitic capacitor between the power supply line andthe reference current setting line (a sixth configuration).

Preferably, in the semiconductor device having the sixth configuration,in plan view of the semiconductor device, the power supply line and thereference current setting line are laid one above another so as topartially overlap with each other (a seventh configuration).

Preferably, in the semiconductor device having the seventhconfiguration, in plan view of the semiconductor device, a part of thereference current setting line that overlaps with the power supply lineis laid in a grid pattern (an eighth configuration).

Preferably, in plan view of the semiconductor device having the eighthconfiguration, in a region enclosed by the reference current settingline laid in the grid pattern, a transistor is formed which functions asa reference current source of the operational amplifier (a ninthconfiguration).

Preferably, in the semiconductor device having the ninth configuration,the transistor is composed of a plurality of unit transistors, and inplan view of the semiconductor device, the plurality of unit transistorsare respectively formed in a plurality of regions enclosed by thereference current setting line laid in the grid pattern (a tenthconfiguration).

Preferably, in plan view of the semiconductor device having any one ofthe eighth to tenth configuration, a proportion of an area occupied bythe power supply line in a region enclosed by the reference currentsetting line laid in the grid pattern is equal to or more than ½ (aneleventh configuration).

Preferably, in the semiconductor device having any one of the sixth toeleventh configurations, the reference current setting line is laidusing a first wiring layer, the power supply line is laid using a secondwiring layer, the capacitor is formed in a region where the power supplyline and the reference current setting line overlap with each other,with the first wiring layer and the second wiring layer as electrodes,and with an insulating layer laid between the electrodes as a dielectricbody (a twelfth configuration).

Preferably, the semiconductor device having any one of the fourth totwelfth configurations further includes a shield member inserted betweenthe power supply line and each of another wiring and another element (athirteenth configuration).

Preferably, in the semiconductor device having the thirteenthconfiguration, the shield member is the ground line (a fourteenthconfiguration).

Preferably, in the semiconductor device having any one of the fourth tofourteenth configurations, a width of the ground line and a width of thereference current setting line are each narrower than a width of thepower supply line (a fifteenth configuration).

Preferably, in the semiconductor device having the fifteenthconfiguration, the width of the ground line and the width of thereference current setting line are each equal to or less than half thewidth of the power supply line (a sixteenth configuration).

Preferably, the semiconductor device having any one of the fourth tosixteenth configurations includes, integrated therein, a plurality ofchannels of the operational amplifier (a seventeenth configuration).

Preferably, in the semiconductor device having the seventeenthconfiguration, external terminals for a first channel are provided on afirst side of a package, and external terminals for a second channel areprovided on a second side of the package (an eighteenth configuration).

An electronic appliance disclosed herein includes the semiconductordevice having any one of the fourth to eighteenth configurations (anineteenth configuration).

A vehicle disclosed herein includes the electronic appliance having thenineteenth configuration (a twentieth configuration).

Advantageous Effects of the Invention

The invention disclosed herein makes it possible to provide anoperational amplifier excellent in noise characteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for illustrating a basic concept of improving noisecharacteristic by means of impedance adjustment.

FIG. 2 is a diagram showing how a low-pass filter is formed inside anoperational amplifier by using resistors.

FIG. 3 is a diagram showing a first embodiment of a semiconductordevice.

FIG. 4 is a diagram showing a configuration example of an operationalamplifier.

FIG. 5 is a diagram showing a second embodiment of a semiconductordevice.

FIG. 6 is a diagram showing a configuration example of a referencecurrent setting portion.

FIG. 7 is a vertical sectional view of a pnp bipolar transistor.

FIG. 8 is a vertical sectional view of an npn bipolar transistor.

FIG. 9 is a diagram showing an example of a wiring layout.

FIG. 10 is a diagram showing a measurement circuit used in a DPI test.

FIG. 11 is a diagram showing a measurement circuit used in a radioemission test.

FIG. 12 is a diagram showing an example of a DPI test result.

FIG. 13 is a diagram showing an example of a radio emission test result.

FIG. 14 is a terminal arrangement diagram showing a third embodiment ofa semiconductor device.

FIG. 15 is a bonding diagram showing a semiconductor device.

FIG. 16 is a plan view showing an example of a wiring layout and of apad arrangement.

FIG. 17 is a vertical sectional view showing a formation example of acapacitor.

FIG. 18 is an exterior view of a vehicle.

DESCRIPTION OF EMBODIMENTS

<Basic Concept>

FIG. 1 is a diagram for illustrating a basic concept of improving noisecharacteristics of an operational amplifier by means of impedanceadjustment.

As shown in the figure, main examples of a noise signal externally fedto an operational amplifier 1 of the present configuration exampleinclude a noise signal NO fed to the power supply terminal VCC, a noisesignal N1 fed to the non-inverting input terminal IN+, and a noisesignal N2 fed to the inverting input terminal IN− as a result of shakingof the output terminal OUT or interference from a noise input line.

To cope with these signals, the operational amplifier 1 of the presentconfiguration example includes a resistor R0 (=corresponding to a powersupply resistor) connected to the power supply terminal VCC, andresistors R1 and R2 (=corresponding to input resistors) which arerespectively connected to the non-inverting input terminal IN+ and theinverting input terminal IN−. With such a configuration, the terminalimpedance of each of the power supply terminal VCC, the non-invertinginput terminal IN+, and the inverting input terminal IN− can be raisedto suppress input of the noise signals NO to N2.

FIG. 2 is a diagram showing how a low-pass filter (what is called an EMI(electromagnetic interference) filter) is formed inside the operationalamplifier 1 by using the resistors R0 to R2.

As shown in the figure, the resistor R0 forms a low-pass filter togetherwith a parasitic capacitor C0 of the power supply line of theoperational amplifier 1. The resistors R1 and R2 respectively formlow-pass filters together with parasitic capacitors C1 and C2 of pnpbipolar transistors Q1 and Q2, respectively, which forms the input stageof the operational amplifier 1.

Thus, in the operational amplifier 1 of the present configurationexample, the parasitic capacitors of various components of theoperational amplifier 1 are used as constituent elements of the low-passfilters. With such a configuration, there is no need of separatelyadding a capacitor to form a low-pass filter, and this helps preventinviting problems such as deterioration of phase margin and increase ofcircuit area in the operational amplifier 1.

Here, the resistance value R of each of the resistors R1 and R2 can beset based on formula (1) below, using the capacitance value C of theparasitic capacitors C1 and C2, respectively, and the target cutofffrequency fc of a corresponding one of the low-pass filters.

R=1/(2π·fc·C)  (1)

For example, in a case where C=8.5 pF and fc=20 MHz, the resistancevalue R can be set such that R≈900Ω.

Here, basically, the resistance value of the resistor R0 can also be setbased on formula (1) above. However, since the resistor R0 is insertedin the power supply line of the operational amplifier 1, in setting itsresistance value, full attention should be paid to preventing the powersupply voltage of the operational amplifier 1 from falling below thelower-limit driving voltage of the operational amplifier 1. In a casewhere only a minimal resistor can be used as the resistor R0, along withthe parasitic capacitor C0, a minimum number of capacitors necessary maybe separately added.

Semiconductor Device (First Embodiment)

FIG. 3 is a block diagram showing a first embodiment of a semiconductordevice. A semiconductor device 10 of the present embodiment is what iscalled an operational amplifier IC, which is a monolithic semiconductorintegrated circuit device, and includes, integrated therein, anoperational amplifier 1, a reference current setting portion 2, a powersupply line L1, a ground line L2, a reference current setting line L3,an output line L4, and electrostatic protection diodes D1 and D2.

The semiconductor device 10 further includes, as means for establishingelectrical connection with outside the device, a plurality of externalterminals (a power supply terminal VCC, a non-inverting input terminalIN+, an inverting input terminal IN−, a ground terminal VEE, and anoutput terminal OUT).

As described previously, the operational amplifier 1 includes resistorsR1 and R2 which form low-pass filters together with unillustratedparasitic capacitors C1 and C2 (see FIG. 2). More specifically, thenon-inverting input node (+) of the operational amplifier 1 isconnected, via the resistor R1, to the non-inverting input terminal IN+of the semiconductor device 10. The inverting input node (−) of theoperational amplifier 1 is connected, via the resistor R2, to theinverting input terminal IN− of the semiconductor device 10. Here, thepresent figure illustrates an example where an operational amplifier 1having one channel is integrated in the semiconductor device 10, but anoperational amplifier 1 having a plurality of channels may instead beintegrated in the semiconductor device 10.

The reference current setting portion 2 sets a reference current Iref,which flows inside the operational amplifier 1. The circuitconfiguration of the reference current setting portion 2 will bedescribed later.

The power supply line L1 is laid between the power supply terminal VCCof the semiconductor device 10 and the power supply node of each of theoperational amplifier 1 and the reference current setting portion 2. Theground line L2 is laid between the ground terminal VEE of thesemiconductor device 10 and the ground node of each of the operationalamplifier 1 and the reference current setting portion 2. The referencecurrent setting line L3 is laid between the reference current settingnode of the operational amplifier 1 and the output node of the referencecurrent setting portion 2. The output line L4 is laid between the outputnode of the operational amplifier 1 and the output terminal OUT of thesemiconductor device 10.

The cathode of the electrostatic protection diode D1 is connected to thenon-inverting input terminal IN+ of the semiconductor device 10. Thecathode of the electrostatic protection diode D2 is connected to theinverting input terminal IN− of the semiconductor device 10. The anodesof the electrostatic protection diodes D1 and D2 are both connected tothe ground terminal VEE of the semiconductor device 10. With thisconfiguration having the electrostatic protection diodes D1 and D2, ahigh surge resistance can be achieved.

Now, many common semiconductor devices have a bypass capacitor (forexample, 100 pF) inserted between the power supply terminal and theground terminal to regulate the power supply voltage. However, theinventors of the present invention have found, through earnest studies,that if a bypass capacitor is inserted between the power supply terminalVCC and the ground terminal VEE of a semiconductor device 10, the inputimpedance of the power supply terminal VCC with respect to highfrequency signals decreases, so that it becomes more likely for noisesignals (high frequency signals) to reach the power supply node of anoperational amplifier 1, to degrade the noise characteristics of theoperational amplifier 1.

Thus, in the semiconductor device 10 of the present embodiment, asindicated by a short-dash line in the present figure, no bypasscapacitor is connected between the power supply terminal VCC and theground terminal VEE, and furthermore, the parasitic capacitor betweenthe power supply line L1 and the ground line L2 is minimized (forexample, 20 pF or lower). With such a configuration, the input impedanceof the power supply terminal VCC with respect to high frequency signalsincreases, so that it becomes less likely for noise signals to reach thepower supply node of the operational amplifier, and this helps improvethe noise characteristics of the operational amplifier 1.

FIG. 4 is a diagram showing a configuration example of the operationalamplifier 1. The operational amplifier 1 of the present configurationexample includes, in addition to the above-mentioned pnp bipolartransistors Q1 and Q2, pnp bipolar transistors Q3 to Q6, npn bipolartransistors Q7 to Q13, a resistor R3, a capacitor C3, and currentsources I1 to I7. The current sources I1 to I7 each pass the referencecurrent Iref (or a constant current corresponding to it) set by thereference current setting portion 2.

First terminals of the current sources I1 to I3 are connected to thepower supply terminal VCC. A second terminal of the current source I1 isconnected to the emitter of the transistor Q2 and the base of thetransistor Q3. A second terminal of the current source I2 is connectedto the emitters of the transistors Q3 and Q4. A second terminal of thecurrent source I3 is connected to the emitter of the transistor Q1 andthe base of the transistor Q4.

The base of the transistor Q1 is connected to the non-inverting inputterminal IN+ via the resistor R1 (see FIG. 2 or FIG. 3), which is notshown in the present figure. The base of the transistor Q2 is connectedto the inverting input terminal IN−via the resistor R2 (see FIG. 2 orFIG. 3), which is not shown in the present figure. The collectors of thetransistors Q1 and Q2 are both connected to the ground terminal VEE.

The collector of the transistor Q3 is connected to the collector of thetransistor Q7. The collector of the transistor Q4 is connected to thecollector of the transistor Q8. The bases of the transistors Q7 and Q8are both connected to the collector of the transistor Q7. The emittersof the transistors Q7 and Q8 are both connected to the ground terminalVEE.

The thus connected current sources I1 to I3, the transistors Q1 to Q4,and the transistors Q7 and Q8 form the input stage, or the amplificationstage, of the operational amplifier 1.

First terminals of the current sources I4 and I5 are both connected tothe power supply terminal VCC. A second terminal of the current sourceI4 is connected to the emitter of the transistor Q5 and the base of thetransistor Q9. A second terminal of the current source I5 is connectedto the collector of the transistor Q9.

The base of the transistor Q5 is connected to the collector of thetransistor Q8 and a first terminal of the capacitor C3. A secondterminal of the capacitor C3 is connected to the collector of thetransistor Q10. The emitter of the transistor Q9 is connected to thebase of the transistor Q10. The collector of the transistor Q5 and theemitter of the transistor Q10 are both connected to the ground terminalVEE.

A first terminal of the current source 16 and the collectors of thetransistor Q12 and Q13 are all connected to the power supply terminalVCC. A second terminal of the current source 16 is connected to thecollectors of the transistor Q10 and Q11 and the base of the transistorQ12. The emitter of the transistor Q12 is connected to the base of thetransistor Q13. The emitter of the transistor Q13 is connected to thebase of the transistor Q11 and a first terminal of the resistor R3.

The emitters of the transistor Q6 and Q11, a second terminal of theresistor R3, and a first terminal of the current source I7 are allconnected to the output terminal OUT. The base of the transistor Q6 isconnected to the collector of the transistor Q10. A second terminal ofthe current source I7 and the collector of the transistor Q6 are bothconnected to the ground terminal VEE.

The thus connected current sources I4 to I7, the transistors Q5 and Q6,the transistors Q9 to Q13, the capacitor C3, and the resistor R3 formthe output stage of the operational amplifier 1.

It should be noted that the circuit configuration shown in the presentfigure is merely an example, and any circuit configuration may beadopted as long as it can achieve a desired operation as the operationalamplifier 1.

Semiconductor Device (Second Embodiment)

FIG. 5 is a diagram showing a second embodiment of the semiconductordevice 10. The semiconductor device 10 of the present embodiment isbased on the first embodiment (FIG. 3) discussed above, but is differentfrom the first embodiment in that a capacitor C4 is further includedwhich is connected between the power supply line L1 and the referencecurrent setting line L3.

With such a configuration, the power supply line L1 and the referencecurrent setting line L3 can be made to fluctuate in the same behaviorwhen noise is fed to the power supply terminal VCC, and thus thebase-emitter voltage of a transistor Q14 is maintained constant. As aresult, the reference current Iref (not shown) flowing inside theoperational amplifier 1 becomes unlikely to be affected by noise, andthus the noise characteristics of the operational amplifier 1 can beimproved.

FIG. 6 is a diagram showing a configuration example of the referencecurrent setting portion 2. As shown in the present figure, the referencecurrent setting portion 2 of the present configuration example includesthe pnp bipolar transistor Q14 and an npn bipolar transistor Q16. Theoperational amplifier 1 further includes a pnp bipolar transistor Q15.

The emitters of the transistors Q14 and Q15 are both connected to thepower supply terminal VCC. The bases of the transistor Q14 and Q15 areboth connected to the collector of the transistor Q14. Thus, thetransistor Q14 and Q15 function as a current mirror that generates acollector current of the transistor Q15 by copying a collector currentof the transistor Q14 at a predetermined mirror ratio (for example, 10times).

Here, the collector current of the transistor Q15 is made to flow to theaforementioned current sources I1 to I7 (see FIG. 4) as the referencecurrent Iref of the operational amplifier 1. That is, the transistorQ15, which is illustrated in the present figure as if it were a singleelement, is actually composed of a plurality of unit transistors, andcurrent mirrors each formed by using one of the unit transistorsfunction as the current sources I1 to I7.

The collector of the transistor Q14 is connected to the collector of thetransistor Q16. The emitter of the transistor Q16 is connected to theground terminal VEE. To the base of the transistor Q16, a predeterminedbias voltage Vb is applied.

Further, as has been described previously, the capacitor C4 is connectedbetween the power supply line L1 and the reference current setting lineL3. Accordingly, even if noise is fed to the power supply terminal VCC,the power supply line L1 and the reference current setting line L3 canbe made to fluctuate in a similar manner, and this makes it possible tomaintain the base-emitter voltage of the transistor Q14 at a constantvalue.

However, as shown in FIG. 7, the transistor Q14 has a parasiticcapacitor Cx between its emitter (=a high-concentration p-typesemiconductor region P+) and its base (=n-type buried layer B/L, whichis a high-concentration n-type semiconductor region N+, and an epitaxialgrowth layer EPI, which is a low-concentration n-type semiconductorregion N−). This applies also to the transistor Q15.

Further, as shown in FIG. 8, the transistor Q16 has a parasiticcapacitor Cy between its collector (=an n-type buried layer B/L, whichis a high-concentration n-type semiconductor region N+, and an epitaxialgrowth layer EPI, which is a low-concentration n-type semiconductorregion N−) and its p-type semiconductor substrate (=P-sub).

Furthermore, a parasitic capacitor Cz is formed between the referencecurrent setting line L3 and the ground line L2.

In view of the presence of the above-described parasitic capacitors Cxto Cz, it is preferable to set the capacitance value of the capacitor C4based on formula (2) below.

C4=(Cy+Cz)−Cx  (2)

For example, in a case such that Cx=550 fF, Cy=700 fF, and Cz=50 fF, thecapacitance value of the capacitor C4 can be set such that C4=200 fF.

By performing such capacitance adjustment, the line-to-line capacitancevalue between the power supply line L1 and the reference current settingline L3 can be made equal to that between the reference current settingline L3 and the ground line L2, and thus the most can be made of thepreviously mentioned effect of making the power supply line L1 and thereference current setting line L3 fluctuate in a similar manner whennoise is fed to the power supply terminal VCC.

<Wiring Layout>

FIG. 9 is a plan view schematically showing an example of a wiringlayout in the semiconductor device 10 of the second embodiment. Here, inthe present figure, the power supply line L1 (width w1) and the groundline L2 (width w2), which are laid in a second wiring layer, areillustrated with solid lines, and the reference current setting line L3(width w3) laid in a first wiring layer (which is directly under thesecond wiring layer) is illustrated with short-dash lines in asee-through manner. As to the widths w1 to w3, it is preferable todesign such that the width w3 of the reference current setting line L3is equal to or less than half the width w1 of the power supply line L1;for example, the widths can be set such that w1=20 μm, w2=5 μm, and w3=5μm.

In the wiring layout shown in the present figure, the power supply lineL1 and the reference current setting line L3 are laid one above theother so as to partially overlap with each other in plan view of thesemiconductor device 10. More specifically, the reference currentsetting line L3 is not laid along the shortest route (which is, in thepresent figure, the route orthogonal to the power supply line L1)between the operational amplifier 1 and the reference current settingportion 2, but is laid along a bypass route part of which is parallel tothe power supply line L1. Further, by laying the reference currentsetting line L3 and the power supply line L1 such that their centersoverlap with each other, generation of noise can be further reduced.

The adoption of such a wiring layout makes it possible to use, as theaforementioned capacitor C4, the parasitic capacitor formed between thepower supply line L1 and the reference current setting line L3.

The capacitance value of the capacitor C4 is calculated from thedielectric constant in vacuum 60 (=8.85×10⁻¹²), the relative dielectricconstant of the interlayer insulation film (such as a SiN film)separating the power supply line L1 from the reference current settingline L3, and the overlapping area S over which the power supply line L1and the reference current setting line L3 overlap with each other, basedon formula (3) below.

C4=ε0×εr×S/d  (3)

Accordingly, for example, in the semiconductor device 10 where εr=6.0and d=10000 Å, in a case where adjustment such that C4≈200 fF isdesired, the adjustment can be achieved by laying the power supply lineL1 and the reference current setting line L3 such that S=3800 μm².

Further, it is desirable to lay the power supply line L1 as far away aspossible from a wiring 3 and an element 4, which are not connected tothe power supply line L1. The power supply node of the operationalamplifier 1 is preferably disposed at a positions as far away aspossible from the other nodes (=such as the input node and the outputnode).

Furthermore, it is desirable to lay a shield member (in the presentfigure, the ground line L2) between the power supply line L1 and each ofthe wiring 3 and the element 4 to prevent mutual electromagneticinterference. In doing so, it is desirable to design such that aline-to-line distance dx between the power supply line L1 and the groundline L2 has a sufficiently large value (for example, 10 μm). In otherwords, the line-to-line distance dx is preferably larger than the widthw2 of the ground line L2. Furthermore, it is preferable to arrange theground line L2 at the center between the wiring 3 and the power supplyline L1, but the ground line L2 may be arranged closer to the wiring 3.

With such a wiring layout, mainly a parasitic capacitor (=the capacitorC4) formed between the lines L1 and L3 and a parasitic capacitor formedbetween the lines L1 and L2 function as the parasitic capacitor of thepower supply line L1. Accordingly, the electromagnetic interference fromthe power supply line L1 to the wiring 3 and the element 4 is reduced,and this helps improve the noise characteristics of the operationalamplifier 1.

<Noise Characteristics Evaluation>

FIG. 10 and FIG. 11 are diagrams showing measurement circuits for a DPI(direct power injection) test and a radio emission test, respectively,conducted with the semiconductor device 10 as the DUT (device undertest).

As shown in FIG. 10, a measurement circuit 100 for the DPI testincludes, in addition to the semiconductor device 10 as the DUT, asignal generator 101, an amplifier 102, an attenuator 103, a bias tee104, a battery 105 (for example, Vcc=12 V), a direct current powersupply 106 (for example, Vin=6 V), and an oscilloscope 107.

The power supply terminal VCC of the semiconductor device 10 isconnected to the output node of the bias tee 104 via a coaxial cable(impedance: 50Ω) having an SMA (sub miniature type A) connector. Thenon-inverting input terminal IN+ of the semiconductor device 10 isconnected to the output node of the direct current power supply 106 viaa coaxial cable (impedance: 50Ω) having an SMA connector. The invertinginput terminal IN− and the output terminal OUT of the semiconductordevice 10 are short-circuited.

In the DPI test using the measurement circuit 100, a noise signal havinga predetermined strength (for example, 17 dBM) is directly injected intothe power supply terminal VCC of the semiconductor device 10. At thattime, by sequentially reading the output voltage appearing at the outputterminal OUT of the semiconductor device 10 while sweeping the frequencyof the noise signal in a predetermined range (for example, 1 MHz to 1GHz), a plot of frequency vs output voltage can be obtained.

As shown in FIG. 11, a measurement circuit 200 for the radio emissiontest includes, in addition to the semiconductor device 10 as the DUT, asignal generator 201, an amplifier 202, an antenna 203, a pseudo-powersupply 204 (for example, Vcc=12 V), a wire harness 205, and anoscilloscope 206. Among these, the antenna 203, the pseudo-power supply204, the wire harness 250, and the semiconductor device 10 as the DUTare all arranged in an anechoic chamber 207.

In the radio emission test using the measurement circuit 200, a noisesignal having a predetermined electric-field strength (for example, 200V/m) is radiated from the antenna 203 toward the noise injection pointof the wire harness 205. Here, the total length of the wire harness 205is 150 cm, and the distance from the noise injection point to thesemiconductor device 10 is 75 cm. The distance from the antenna 203 tothe noise injection point is 100 cm. These dimensions are based on ISO11452-2.

In the above measurement circuit 200, with the wire harness 205connected to the power supply terminal VCC of the semiconductor device10, the noise signal is indirectly injected into the power supplyterminal VCC of the semiconductor device 10. At that time, bysequentially reading the output voltage appearing at the output terminalOUT of the semiconductor device 10 while sweeping the frequency of thenoise signal in a predetermined range (for example, 200 MHz to 1 GHz), aplot of frequency vs output voltage can be obtained.

FIG. 12 and FIG. 13 are diagrams respectively showing examples ofresults of the DPI test and the radio emission test. In each of thefigures, the horizontal axis (the logarithmic axis) represents thefrequency of the noise signal, and the vertical axis represents theoutput voltage of the semiconductor device 10.

The solid line in each of the figures indicates the result of a testperformed with the semiconductor device 10 of the second embodiment(FIG. 5) as the DUT. On the other hand, the short-dash line in each ofthe figures indicates the result of a test performed with a conventionaloperation amplifier (=without the resistors R1 and R2, without thecapacitor C4, with a bypass capacitor) as the DUT.

The test condition in FIG. 12 is as follows; the noise applicationlevel: 17 dBm, the frequency: 100 MHz to 1 GHz. The test condition inFIG. 13 is as follows; the measurement circuit: a voltage follower, Vcc:12 V, Vin: 6 V, the temperature: room temperature, the test method:substitution method (traveling-wave power), electric-field strength: 200V/m, the test wave: CW (continuous wave), frequency: 200 MHz to 1 GHz(2% step).

As is clear from each of these figures, with the semiconductor device 10of the second embodiment (FIG. 5), in whichever test, no peak exceeding±5% appears over the entire frequency-sweeping range. Thus, thesemiconductor device 10 of the second embodiment (FIG. 5) has excellentnoise characteristics, and its output varies very little even when anoise is fed thereto. This contributes to providing simple measuresagainst noise in a set in which the semiconductor device 10 is mounted,making the set very handy.

Semiconductor Device (Third Embodiment)

FIG. 14 is a terminal arrangement diagram showing a third embodiment ofa semiconductor device. A semiconductor device 10 of the presentembodiment has two channels of operational amplifiers 1 a and 1 b (=eachcorresponding to the operational amplifier 1 discussed previously)integrated therein. Here, for convenience of illustration, componentsother than the operational amplifiers 1 a and 1 b are not shown.

Further, as the package of the semiconductor device 10, there may beadopted an SOP (Small Outline Package), an SSOP (Shrink SOP), or, anMSOP (Micro SOP), each having four terminals derived from each of twoopposite sides thereof, thus a total of eight external terminals (pin-1to pin-8) derived therefrom. In the present figure, pin-1 to pin-4 areprovided on a first side of the package, and pin-5 to pin-8 are providedon a second side of the package.

Pin-1 is the output terminal OUT1 of a first channel, and is connectedto the output terminal of the operational amplifier 1 a. Pin-2 is theinverting input terminal IN1− of the first channel, and is connected tothe inverting input terminal (−) of the operational amplifier 1 a. Pin-3is the non-inverting input terminal IN1+ of the first channel, and isconnected to the non-inverting input terminal (+) of the operationalamplifier 1 a. Pin-4 is the ground terminal VEE.

Pin-5 is the non-inverting input terminal IN2+ of the second channel,and is connected to the non-inverting input terminal (+) of theoperational amplifier 1 b. Pin-6 is the inverting input terminal IN2− ofthe second channel, and is connected to the inverting input terminal (−)of the operational amplifier 1 b. Pin-7 is the output terminal OUT2 ofthe second channel, and is connected to the output terminal of theoperational amplifier 1 b. Pin-8 is the power supply terminal VCC.

Thus, the external terminals (pin-1 to pin-3) of the first channel areall provided on the first side of the package, and the externalterminals (pin-5 to pin-7) of the second channel are all provided on thesecond side of the package.

Here, although the present figure deals with an example where the twochannels of operational amplifiers 1 a and 1 b are integrated, but it isalso possible to integrate four-channel operational amplifiers. In thatcase, for example, an SOP, an SOP or an MSOP, each having 14 pins, canbe preferably used.

FIG. 15 is a bonding diagram showing bonding inside the package of thesemiconductor device 10. In the semiconductor device 10, the operationalamplifiers 1 a and 1 b, etc. are integrated in a semiconductor chip 300,which is mounted on an island 310 and sealed in that state with a moldresin 320. In the following description, the upward, downward, leftward,and rightward directions in the sheet on which the figure is drawn aredefined as the upward, downward, leftward, and rightward directions inplan view of the semiconductor device 10 (or the semiconductor chip300).

The semiconductor chip 300 has eight pads P1 to P8. The pad P1 is a padcorresponding to the output terminal of the operational amplifier 1 a,and is connected to a leading end side of pin-1 (OUT1) via a wire W1.The pad P2 is a pad corresponding to the inverting input terminal (|) ofthe operational amplifier 1 a, and is connected to pin-2 (IN1−) via awire W2. The pad P3 is a pad corresponding to the inverting inputterminal (+) of the operational amplifier 1 a, and is connected to pin-3(IN1+) via a wire W3. The pad P4 is a ground pad, and is connected to aleading end side of pin-4 (VEE) via a wire W4.

The pad P5 is a pad corresponding to the non-inverting input terminal(+) of the operational amplifier 1 b, and is connected to pin-5 (IN2+)via a wire W5. The pad P6 is a pad corresponding to the inverting inputterminal (−) of the operational amplifier 1 b, and is connected to pin-6(IN2−) via a wire W6. The pad P7 is a pad corresponding to the outputterminal of the operational amplifier 1 b, and is connected to a leadingend side of pin-7 (OUT2) via a wire W7. The pad P8 is a power supplypad, and is connected to a leading end side of pin-8 (VCC) via a wireW8.

The pads P1 to P8 are arranged along the outer edge of the semiconductorchip 300 in order corresponding to the order in which pin-1 to pin-8 arearranged. Accordingly, the wires W1 to W8 each connecting a pad and apin corresponding to the pad can each be laid at the shortest distance.

In terms of the frame area inside the package, pin-1 (OUT1), pin-4(VEE), pin-5 (IN2+), and pin-8 (VCC) are all larger than any of pin-2(IN−), pin-3 (IN1+), pin-6 (IN2−), and pin-7 (OUT2).

That is, in terms of the upward and downward directions in the sheet onwhich the figure is drawn, pin-1 (OUT1) and pin-4 (VEE) each have aportion projecting more than pin-2 (IN1−) and pin-3 (IN1+). Likewise,pin-5 (IN2+) and pin-8 (VCC) each have a portion projecting more thanpin-6 (IN2−) and pin-7 (OUT2).

Further, in terms of the leftward and rightward directions in the sheeton which the figure is drawn, pin-1 (OUT1) and pin-4 (VEE) each have apart thereof overlapping with an island 310. Likewise, pin-5 (IN2+) andpin-8 (VCC) each have a part thereof overlapping with the island 310.

Furthermore, between pin-1 (OUT) and pin-8 (VCC) and between pin-4 (VEE)and pin-5 (IN2+), there are formed support frames 330 and 340,respectively, to support the island 310.

FIG. 16 is a plan view showing an example of a wiring layout and a padarrangement (around the operational amplifier 1 a) on the semiconductorchip 300. Here, in the present figure, the power supply line L1 (widthw1) and the ground line L2 (width w2) laid in the second wiring layerare each illustrated with solid lines (hatching regions), and thereference current setting line L3 (width w3) laid in the first wiringlayer (=directly under the second wiring layer) is illustrated inshort-dash line in a see-through manner. As to the widths w1 to w3 ofthese lines, it is preferable to design such that the width w2 of theground line L2 and the width w3 of the reference current setting line L3are each narrower than (for example, equal to or less than half) thewidth w1 of the power supply line L1, for example, such that w1=20 μm,w2=5 μm, and w3=5 μm.

In the following description, the upward, downward, leftward, andrightward directions in the sheet on which the figure is drawn aredefined as the upward, downward, leftward, and rightward directions inplan view of the semiconductor chip 300, and the wiring layout and thepad arrangement will be described with reference also to FIG. 4, FIG. 6,and FIG. 15, as necessary, which have been referred to previously.

As pads relating to the operational amplifier 1 a, the present figureillustrates the pads P1 to P4, and P8. Here, in the plan view of thesemiconductor chip 300, the positions at which the pads P1 to P4 and P8are provided correspond to the positions indicated in FIG. 15 referredto previously.

Specifically, as to the pads P1 to P3, in plan view of the semiconductorchip 300, the pad P1, the pad P2, and the pad P3 are arranged in thisorder from the right side toward the left side of the sheet on which thefigure is drawn.

More specifically, the pad P1 is provided near the upper right corner ofthe semiconductor chip 300. The pad P2 is provided near the upper sideof the semiconductor chip 300, at a position slightly to the left of thecenter in the left-right direction. The pad P3 is provided near theupper left corner of the semiconductor chip 300.

Of the pads P1 to P3, the pad P1 is located farthest from the upper sideof the semiconductor chip, and the pad P3 is located nearest to theupper side of the semiconductor chip 300. That is, where a distancebetween the pad P1 and the upper side of the semiconductor chip 300 isrepresented by d1 x, a distance between the pad P2 and the upper side ofthe semiconductor chip 300 is represented by d2, and a distance betweenthe pad P3 and the upper side of the semiconductor chip 300 isrepresented by d3 x, d1 x>d2>d3 x holds.

Further, a distance d1 y between the pad P1 and the right side of thesemiconductor chip 300 is longer than a distance d3 y between the pad P3and the left side of the semiconductor chip 300 (d1 y>d3 y).

A distance d12 between the pads P1 and P2 is longer than a distance d23between the pads P2 and P3 (d12>d23).

In plan view of the semiconductor chip 300, the pad P4 is provided nearthe left side of the semiconductor chip 300, substantially at the centerin the up-down direction. Here, a distance d4 between the pad P4 and theleft side of the semiconductor chip 300 is substantially equal to thedistance d3 y between the pad P3 and the left side of the semiconductorchip 300 (d4≈d3 y).

In plan view of the semiconductor chip 300, the pad P8 is provided nearthe right side of the semiconductor chip 300, substantially at thecenter in the up-down direction. Here, a distance d8 between the pad P8and the right side of the semiconductor chip 300 is shorter than thedistance d1 y between the pad P1 and the right side of the semiconductorchip 300 (d8<d1 y).

Here, the pads P1 to P3 are all arranged within the region where theoperational amplifier 1 a is formed. On the other hand, the pad P4 isarranged in the region where the reference current setting portion 2 isformed.

The power supply line L1 is laid from the pad P8 (VCC) toward theemitters of the transistors Q14 and Q15 and various components (such asa power transistor POW) of the operational amplifier 1 a. Specifically,the power supply line L1 first extends from the pad P8 toward the upperside of the semiconductor chip 300, and then branches into a first lineL1 a extending toward the upper side of the semiconductor chip 300 and asecond line L1 b extending toward the left side of the semiconductorchip 300. In the branching portion from which the first line L1 a andthe second line L1 b extend separately, a tapered portion L1 x is formedat the upper left corner. Further, near the pad P8 (VCC), anelectrostatic protection element ESD is formed.

The first line L1 a, after being separated from the second line L1 b, isbent toward the right side of the semiconductor chip 300. On the otherhand, the second line L1 b, after the transistor POW, branches into athird line L1 c, which changes the direction of its course to adirection toward the lower side of the semiconductor chip and furtherextends toward the emitter of the transistor Q14, and a fourth line L1d, which continuously extends in a direction toward the left side of thesemiconductor chip 300 and further extends toward the emitter of thetransistor Q15. Here, within the range where the transistor Q15 isformed, the fourth line L1 d is formed in a comb teeth shape. The teethparts (the parts projecting in the up-down direction) and the main axispart (the part extending in the left-right direction) of the thus formedfourth line L1 d, are respectively connected to the emitters of aplurality of unit transistors of the transistor Q15. Thus, thetransistor Q15 is composed of the plurality of unit transistors, andcurrent mirrors formed by using the unit transistors function as thecurrent sources I1 to I7 (see FIG. 4 referred to previously).

The ground line L2 is laid from the pad P4 (VEE) toward variouscomponents of the semiconductor chip 300. Specifically, the ground lineL2 first extends from the pad P4 toward the upper side of thesemiconductor chip 300, then, before the pad P3, changes the directionof its course to a direction toward the right side of the semiconductorchip 300, passes through a region between the power supply line L1 andthe pads P1 to P3, while being bent several times, and then reaches aposition near the right side of the semiconductor chip 300.

The reference current setting line L3 is laid between the bases of thetransistors Q14 and Q15, which are arranged side by side in the up-downdirection of the semiconductor chip 300. More specifically, thereference current setting line L3 is laid not only along the shortestroute between the bases of the transistors Q14 and Q15 but also along abypass route, part of which is parallel to the power supply line L1 (thefourth line L1 d). The reference current setting line L3 is also laidsuch that centers of the reference current setting line L3 and the powersupply line L1 (the fourth line L1 d) overlap with each other.

Thus, the power supply line L1 and the reference current setting line L3are laid one above the other so as to partially overlap with each otherin plan view of the semiconductor chip 300 (see, for example, a regionα). This makes it possible to use the parasitic capacitor between thepower supply line L1 and the reference current setting line L3 as thecapacitor C4 described previously.

In particular, in the reference current setting line L3, its partoverlapping with the power supply line L1 is laid in a grid pattern.This wiring layout makes it possible to increase the overlapping areaover which the power supply line L1 and the reference current settingline L3 overlap with each other.

Here, in the grid-pattern part of the reference current setting line L3,the plurality of unit transistors forming the transistor Q15 can berespectively arranged in a plurality of regions β enclosed by thereference current setting line L3.

Further, it is desirable that the proportion of an area occupied by thepower supply line L1 in each of the plurality of regions β be ½ or more.

Further, it is desirable to provide, between the power supply line L1and the pads P1 to P3 (and the constituent elements of the operationalamplifier 1 a connected to these), a shield member (the ground line L2in this figure) that prevents electromagnetic interference between them.

Here, although the illustration in the present figure is focused on theoperational amplifier 1 a, the same wiring layout and the same padarrangement as illustrated in the figure can be adopted also for theoperational amplifier 1 b. Specifically, as is clear from comparisonbetween the pads P1 to P3 and the pads P5 to P7 illustrated in FIG. 15referred to previously, the wiring layout and the pad arrangementdescribed above can be reversed in the up-down direction in the sheet onwhich the figure is drawn.

FIG. 17 is a vertical sectional view showing a formation example of thecapacitor C4 in the region α. As shown in the figure, in the region α ofthe semiconductor chip 300, a p-type semiconductor substrate (P-sub), ann-type buried layer (B/L), an n-type epitaxial growth layer (EPI), ap-type well (P/W), a high-concentration p-type semiconductor region(P+), a first metal layer (1st METAL), an insulation layer (ISO), and atop metal layer (TOP METAL) are formed one on another in this orderupward from the bottom.

Here, the power supply line L1 is laid by using the top metal layer (TOPMETAL), and the reference current setting line L3 is laid by using thefirst metal layer (1st METAL). Accordingly, in the region α where thepower supply line L1 and the reference current setting line L3 overlapwith each other in the vertical direction, the capacitor C4 is formedwith the top metal layer (TOP METAL) and the first metal layer (1stMETAL) as electrodes and the insulation layer (ISO) between these metallayers as a dielectric body.

<Application to Vehicle>

FIG. 18 is an exterior view showing a configuration example of a vehicleX. The vehicle X of the present configuration example has mountedtherein various electronic appliances (X11 to X18) that operate by beingsupplied with a power supply voltage from a battery. Here, forconvenience of illustration, mounting positions of the electronicappliances X11 to X18 in the present figure may be different fromreality.

The electronic appliance X11 is an engine control unit which performsengine-related controls (injection control, electronic throttle control,idling control, oxygen sensor heater control, auto cruise control,etc.).

The electronic appliance X12 is a lamp control unit which performslighting-on-and-off control with respect to an HID (high intensitydischarged lamp), a DRL (daytime running lamp), etc.

The electronic appliance X13 is a transmission control unit whichperforms transmission-related control.

The electronic appliance X14 is a braking unit which performs controls(an ABS (anti-lock brake system) control, an EPS (electric powersteering) control, electronic suspension control, etc.) relating to themotion of the vehicle X.

The electronic appliance X15 is a security control unit which performsdriving control with respect to a door lock, a security alarm, etc.

The electronic appliance X16 is an electronic appliance incorporated inthe vehicle X at the stage of shipment from the factory as standardequipment or as the manufacturer's option item, such as a wiper, anelectric door mirror, a power window, a damper (shock absorber), anelectric sunroof, an electric seat, or the like.

The electronic appliance X17 is an electronic appliance which is mountedas necessary in the vehicle X as a user's option item, such as anin-vehicle A/V (audio/visual) appliance, a car navigation system, an ETC(electronic toll collection) system, or the like.

The electronic appliance X18 is an electronic appliance provided with ahigh voltage motor, such as an in-vehicle blower, an oil pump, a waterpump, a battery cooling fan, or the like.

Note that the operational amplifier IC10 described previously ismountable in any of the electronic appliances X11 to X18.

Other Modified Examples

The embodiments discussed above have dealt with examples where anoperational amplifier is used in an in-vehicle appliance, but this isnot intended to limit the application of the present invention, and thepresent invention is widely and generally applicable to any applicationsincluding home electric appliances, industrial appliances, etc.

Further, in addition to the above embodiments, it is possible to addvarious modifications to the various technical features disclosed hereinwithout departing from the spirit of the technological creation. Forexample, bipolar and MOS field-effect transistors may be interchanged,and the logic level of any signal may be inverted as necessary. That is,it should be understood that the above embodiments are illustrative inall respects and are not intended to limit the present invention; thetechnological scope of the present invention is not indicated by theabove description of the embodiments but by the claims; and allmodifications within the scope of the claims and the meaning equivalentto the claims are covered.

INDUSTRIAL APPLICABILITY

The operational amplifier disclosed herein is usable in, for example,in-vehicle appliances, home electric appliances, and industrialappliances.

LIST OF REFERENCE SIGNS

-   -   1, 1 a, and 1 b operational amplifier    -   2 reference current setting portion    -   3 wiring    -   4 element    -   10 semiconductor device (operational amplifier IC)    -   100 measurement circuit (DPI test)    -   101 signal generator    -   102 amplifier    -   103 attenuator    -   104 bias tee    -   105 battery    -   106 direct current power supply    -   107 oscilloscope    -   200 measurement circuit (radio emission test)    -   201 signal generator    -   202 amplifier    -   203 antenna    -   204 pseudo-power supply    -   205 wire harness    -   206 oscilloscope    -   207 anechoic chamber    -   300 semiconductor chip    -   310 island    -   320 mold resin    -   330, 340 support frame    -   C0, C1, C2, Cx, Cy, Cz parasitic capacitor    -   C3 capacitor    -   C4 capacitor (parasitic capacitor)    -   D1, D electrostatic protection diode    -   ESD electrostatic protection element    -   I1 to I7 current source    -   L1 power supply line    -   L1 a first line    -   L1 b second line    -   L1 c third line    -   L1 d fourth line    -   L1 x tapered portion    -   L2 ground line    -   L3 reference current setting line    -   L4 output line    -   P1 to P8 pad    -   POW power transistor    -   Q1 to Q6, Q14, Q15 pnp bipolar transistor    -   Q7 to Q13, Q16 npn bipolar transistor    -   R0 resistor (power supply resistor)    -   R1, R2 resistor (input resistor)    -   R3 resistor    -   W1 to W8 wire    -   X vehicle    -   X11 to X18 electronic appliance    -   α,β region

1. An operational amplifier comprising: a transistor forming an inputstage; and an input resistor forming a filter together with a parasiticcapacitor of the transistor.
 2. The operational amplifier according toclaim 1, wherein a resistance value R of the input resistor is set basedon a capacitance value C of the parasitic capacitor and a target cutofffrequency fc of the filter such that R=1/(2π·fc·C).
 3. The operationalamplifier according to claim 2, further comprising a power supplyresistor which forms a filter together with a parasitic capacitor of apower supply line.
 4. A semiconductor device comprising: the operationalamplifier according to claim 1; a reference current setting portionconfigured to set a reference current of the operational amplifier; apower supply line laid between a power supply terminal and each of theoperational amplifier and the reference current setting portion; aground line laid between a ground terminal and each of the operationalamplifier and the reference current setting portion; and a referencecurrent setting line laid between the operational amplifier and thereference current setting portion.
 5. The semiconductor device accordingto claim 4, further comprising a capacitor connected between the powersupply line and the reference current setting line.
 6. The semiconductordevice according to claim 5, wherein the capacitor is a parasiticcapacitor between the power supply line and the reference currentsetting line.
 7. The semiconductor device according to claim 6, wherein,in plan view of the semiconductor device, the power supply line and thereference current setting line are laid one above another so as topartially overlap with each other.
 8. The semiconductor device accordingto claim 7, wherein, in plan view of the semiconductor device, a part ofthe reference current setting line that overlaps with the power supplyline is laid in a grid pattern.
 9. The semiconductor device according toclaim 8, wherein, in plan view of the semiconductor device, in a regionenclosed by the reference current setting line laid in the grid pattern,a transistor is formed which functions as a reference current source ofthe operational amplifier.
 10. The semiconductor device according toclaim 9, wherein the transistor is composed of a plurality of unittransistors, and in plan view of the semiconductor device, the pluralityof unit transistors are respectively formed in a plurality of regionsenclosed by the reference current setting line laid in the grid pattern.11. The semiconductor device according to claim 8, wherein, in plan viewof the semiconductor device, a proportion of an area occupied by thepower supply line in a region enclosed by the reference current settingline laid in the grid pattern is equal to or more than ½.
 12. Thesemiconductor device according to claim 6, wherein the reference currentsetting line is laid using a first wiring layer, the power supply lineis laid using a second wiring layer, the capacitor is formed in a regionwhere the power supply line and the reference current setting lineoverlap with each other, with the first wiring layer and the secondwiring layer as electrodes, and with an insulating layer laid betweenthe electrodes as a dielectric body.
 13. The semiconductor deviceaccording to claim 4, further comprising a shield member insertedbetween the power supply line and each of another wiring and anotherelement.
 14. The semiconductor device according to claim 13, wherein theshield member is the ground line.
 15. The semiconductor device accordingto claim 4, wherein a width of the ground line and a width of thereference current setting line are each narrower than a width of thepower supply line.
 16. The semiconductor device according to claim 15,wherein the width of the ground line and the width of the referencecurrent setting line are each equal to or less than half the width ofthe power supply line.
 17. The semiconductor device according to claim4, wherein the semiconductor device comprises, integrated therein, aplurality of channels of the operational amplifier.
 18. Thesemiconductor device according to claim 17, wherein external terminalsfor a first channel are provided on a first side of a package, andexternal terminals for a second channel are provided on a second side ofthe package.
 19. An electronic appliance comprising the semiconductordevice according to claim
 4. 20. A vehicle comprising the electronicappliance according to claim 19.